The seal that is placed over the expansion gap between the sections of a deck structure is designed to keep foreign substances such as debris, water, and chemicals from falling into the gap. Such foreign substances can cause spalling and damage to the deck substructure, especially when they clog up the gap so much that they interfere with the normal expansion of the deck sections. To keep these foreign substances out, it is very important that the seal be fixed in firm sealing engagement with both adjacent deck sections throughout the entire length of the seal.
Vertical fasteners, spaced along the length of the seal, are usually employed to clamp the seal in firm sealing engagement with each deck section. Various types of fasteners may be used, such as a pin embedded in the deck section, with a nut threaded on the pin above the seal, or a collar embedded in the deck section, into which is threaded an anchor bolt having a head used to clamp the seal in place. In this application, the term "anchor bolt" will be used in a broad sense to refer to any of these possible fastening means that are mechanical equivalents of an anchor bolt.
Expansion joint seals are often prone to being loosened or separated from the deck sections to which they are secured. One reason for such problems is that a flat metal plate is often employed under the heads of the seal's anchor bolts to distribute the forces exerted by these bolts across the entire length and width of the seal. This flat metal plate may tend to flex upwardly in some places, causing the adjacent elastomeric portion of the seal to flex upwardly as well.
Another possible reason for the seal loosening is that the heads of the seal's anchor bolts are often tightened against a plate resting on the resilient compression pad of the seal. In such seal assemblies, each anchor bolt is likely to be tightened to a different degree, at least to some extent. This is because of the variations in the elastomeric material and in the surfaces of the deck sections (i.e., high and low spots or voids). Too much tightening of an anchor bolt can cause the seal to lift up in areas that are spaced from but are near the anchor bolt, while too little tightening will of course cause leaking in the immediate area of the anchor bolt.
There are some seals that are clamped to the deck sections by anchor bolts located beyond the lateral edges of the seal and plates that are secured by the anchor bolts and extend from the anchor bolts over the edges of the seal. Examples of such cantilever-type clamping plates are shown in U.S. Pat. No. 3,713,368 to McDowell et al., and an advertisement of a seal assembly manufactured by Fel-Pro, Incorporated on page 7 of the December 1976 issue of Civil Engineering ASCE. The anchor bolts of these seals are tightened against solid metal plates that are in direct contact with the deck sections, so that a workman installing the seal can properly tighten each anchor bolt. However, these metal plates are secured to the deck sections on one side only, and are prone to rocking about their connections with the anchor bolts. With the repeated impacts of the wheels of passing traffic, these plates tend to rock loose and release the tight engagement between the seal and the deck sections.